Electric discharge tube having heat flow cathode centering member



P 1963 F. H- R. ALMER EI'AL 3,086,136

- ELECTRIC DISCHARGE TUBE HAVING HEAT FLOW CATHODE CENTERING MEMBERFiled March 17, 1960 INVENTOR FRIEDRICH H.R.ALMER JAN FENNEMA ADRIANUSKUIPER HENDRIK SANTING JANA. VAN VELDHUIZEN AGENT Unite titres ELECTRICDISCHARGE TUBE HAVING HEAT FLOW CATHODE CENTERING MEMBER FriedrichHermann Raymund Almer, Jan Fennema, Adrianus Kuiper, Hendrik Santing,and Jan Anton van Veldhuizen, all of Eindhoven, Netherlands, assignorsto North American Philips Company, Inc., New York,

N.Y., a corporation of Delaware Filed Mar. 17, 1960, Ser. No. 15,614Claims priority, application Netherlands Apr. 1, 1959 2 Claims. (Cl.313-47) This invention relates to electric discharge tubes havingthermionic cathodes which are centered and supported in the tube bymeans of at' least one preferably plate-shaped insulating member.

It is common knowledge that comparatively large temperature differencescan occur between the ends and the center of thermionic cathodes andthat furthermore the temperature of the cathodes of a number of tubes ofone and the same type can be widely different.

Many attempts have been made to reduce the abovementioned disadvantageby decreasing the heat dissipation of the ends of the cathode by takingsteps for reducing the transfer of heat from the cathode to theinsulating members as far as possible. However, it has been found thatthese steps mitigate the first-mentioned disadvantage, but that thedifference in the cathode temperatures of a number of tubes of one andthe same type could be reduced only in a comparatively small degree.

It has now been found that especially the second disadvantage can beconsiderably reduced if, in accordance with the invention, steps aretaken in such tubes to ensure that the heat transfer of the cathode tothe part of the insulator which is in contact with the cathode exceedsthe heat dissipation from this part of the insulator to the remainingpart. The part of the preferably plate-shaped insulator which engagesthe cathode is connected to the remaining part of the insulator by partswhich poorly conduct heat, so that the heat dissipation through thesemembers is reduced to a minimum. In any case, the temperature gradientalong these connecting parts must exceed the temperature gradientbetween the part of the cathode engaging the insulator and this adjacentpart of the insulator. As a result, the temperature difference betweenthis latter part of the insulator and the cathode becomes comparativelyslight.

The present invention is based on the recognition that the largedifferences in heat dissipation are due to the fact that there is ahighly variable thermal contact between the cathode and the insulatorengaging it so that large variations in the heat dissipation areproduced. By the step in accordance with the present invention, thetemperature of the part of the insulator engaging the cathode becomescomparatively high so that there is only a comparatively slightdifference between the cathode temperature and the insulator temperatureat the points of contact. Differences in the heat transfer at thesepoints consequently have a relatively smaller influence upon the heatdissipation of the cathode.

The heat dissipation of the hot parts of the insulator to the remainingpart of this insulator can be accurately determined and hence keptconstant for the various specimens owing to the fact that this transferis effected through stationary parts of the insulator. These stationaryparts may comprise connecting strips produced by aperturing aplate-shaped insulator. It is desirable for the heat dissipation throughthese strips to be reduced to a minimum, however, in any case, this heatdissipation always is substantially equal for equal insulating members.Furthermore it is desirable for the cathode to be in highlyheatconducting connection with the insulator so that at this point theabrupt thermal variation is small and hence variations in thisconnection exert a lesser influence upon the cathode temperature.

It has been found that the value of the temperature differences in thevarious tubes of one and the same type can be reduced by half or even bytwo-thirds by the use of the invention.

The invention will now be described more fully with reference to adrawing, in which FIG. 1 is a plan view of an electrode system of a tubein accordance with the invention, and

H6. 2 shows an alternative embodiment.

In FIG. 1, reference numeral 1 denotes a tube envelope and 2 a cathode;grid stay rods are designated 3' and bent-over lugs securing the anodeto a mica member 5 are designated 4. Parts 6 of the mica centeringmember 5 are in good thermal contact with the cathode, but are connectedto the remaining part of the plate 5 by narrow strips 7 only. Since theheat dissipation through the parts 7 can be much smaller than that fromthe cathode to the parts 6, the parts 6 will assume a high temperatureand differences in heat dissipation from the cathode 2 to the parts 6will have a smaller influence on the total heat dissipation, since thisis determined by the parts 7 and can be accurately equal for all themica members. The thermal contact between the cathode and the micamember, however, can fluctuate widely since the cathode must not begripped in the aperture of the mica plate too firmly. Small variationsof the sizes of the cathode cross-section and of the mica aperture cangive rise to large diiferences in the thermal contact.

Due to the very slight heat dissipation through these parts 7, thetemperature drop across the cathode from the center to the ends is alsodecreased while the mean cathode temperature is increased.

In FIG. 2, use is made of a separate mica plate 10 which serves inparticular for centering the cathode 2 and the grid stay rod 3. Hereagain the parts 6 of the mica plate can assume a high temperature. Thegrid is centered with respect to the anode 4 and the tube wall 1 bymeans of a mica member 5 which, however, does not engage the cathode.

It will be appreciated that the invention can be carried into effect inalternative manners also. However, a heat accumulation must always bepossible in the part of the mica member engaging the cathode so thatalways the heat transfer from the cathode to the mica must be betterthan the heat dissipation from this part of the mica member to theremaining parts of this member.

What is claimed is:

1. An electric discharge tube comprising at least one electrodeincluding a thermionic cathode, an electrode centering member ofinsulating material having a first portion engaging the cathode and asecond portion in contact with a cooler portion of the tube, saidcentering member having a portion intermediate the first and secondportions thereof which has a smaller sectional area than that of thefirst and second portions whereby the transfer of heat from the firstportion to the second portion is retarded and the temperature differencebetween said first portion and the cathode is minimized.

2. An electric discharge tube as claimed in claim 1, in which thecentering member is a mica plate of which the first portion engaging thecathode is connected to the remainder of the mica plate by narrow stripsonly.

References Cited in the file of this patent UNITED STATES PATENTS1,967,208 Krahl July 17, 1934 2,907,912 Stephens Oct. 6, 1959 2,917,652Van der Poel Dec. 15, 1959

1. AN ELECTRIC DISCHARGE TUBE COMPRISING AT LEAST ONE ELECTRODEINCLUDING A THERMIONIC CATHODE, AN ELECTRODE CENTERING MEMBER OFINSULATING MATERIAL HAVING A FIRST PORTION ENGAGING THE CATHODE AND ASECOND PORTION IN CONTACT WITH A COOLER PORTION OF THE TUBE, SAIDCENTERING MEMBER HAVING A PORTION INTERMEDIATE THE FIRST AND SECONDPORTIONS THEREOF WHICH HAS A SMALLER SECTIONAL AREA THAN THAT OF THEFIRST AND SECOND PORTIONS WHEREBY THE TRANSFER OF HEAT FROM THE FIRSTPORTION TO THE SECOND PORTION IS RETARDED AND THE TEMPERATURE DIFFERENCEBETWEEN SAID FIRST PORTION AND THE CATHODE IS MINIMIZED.